Description (as provided by the applicant): This proposed R13 application covers the next series of meetings of the International Workshop on Opportunistic Protists (i.e. IWOP-12, IWOP-13 and IWOP-14). This meeting is devoted to protists that cause serious problems in patients with defective immune systems, such as those receiving immunosuppressive therapies or with immune system debilitating diseases, such as AIDS. Many of these poorly understood pathogens were initially recognized due to their increased frequency in opportunistic settings, such as in HIV/AIDS and transplantation; however, it is now appreciated that these are also pathogens of immune competent hosts. Several of these organisms, due to their transmission by food and water, are also biodefense category B pathogens and environmental protection agency (EPA) pathogens of interest. The IWOP meeting was initiated in 1988 to serve the small, but growing international scientific community interested in working with the unusual, non-cultivatable organism Pneumocystis. At the time, Pneumocystis was relatively unknown and was ignored by many in the microbiological community. There was a need for a small meeting where scientists could exchange new techniques and experiences gained from working with these 'difficult' organisms. A basic tenet of the IWOP Workshops is a free exchange of information facilitated by open admission to the meeting. The second through eleventh IWOP meetings grew to include other opportunistic organism-based community groups that experience many of the research challenges facing the Pneumocystis community. The IWOP meetings now include research presentations on Cryptosporidia; Microsporidia; Toxoplasma gondii; and free-living amebae that are pathogenic. In recent years, IWOP has also begun serving as a forum for researchers of kinetoplastid flagellates and other eukaryotic microbial parasites that are caused by different genotypes or present pathologies in immune deficient individuals distinct from that observed in immune competent patients. Today, the IWOP meeting is regarded as the most important meeting for most researchers of Pneumocystis, Cryptosporidia, and Microsporidia. It is the meeting at which community based projects (e.g. genome sequencing, animal models, culture techniques, etc.) and consensus papers (i.e. taxonomic status, research priorities, and nomenclature standards) have been developed. It is a critical meeting for these research communities focused on this difficult pathogenic protists. Because many of these organisms are not well represented in larger fungal or parasitology meetings, research progress would clearly be severely hampered if this important forum was no longer held. IWOP-12 is scheduled for August 2012 in Tarrytown, NY, IWOP-13 for August 2014 in Seville, Spain; and IWOP-14 for July 2016 in Cincinnati, Ohio. Public Health Relevance: The International Workshops on Opportunistic Protists (IWOP) is a series of meetings devoted to infections (termed opportunistic infections) that cause serious problems in AIDS patients and other individuals with defective immune systems. The 1st meeting in 1988 was initiated to serve the international scientific community interested in working with the unusual, non-cultivable organism Pneumocystis, which causes pneumonia and is the direct cause of death in many AIDS patients. At the time, Pneumocystis was relatively unknown and was ignored by many in the microbiological community. There was a need for a small meeting where scientists could exchange new techniques and experiences gained from working with these organisms that are difficult to work with in the laboratory. A basic tenet of IWOP is the free exchange of information facilitated by open admission to the meeting. The 2nd through 11th Workshops grew to include other opportunistic organism-based scientific communities that experience many of the same research challenges facing the Pneumocystis community. IWOP now includes research presentations on Cryptosporidium; the Microsporidia, both causing AIDS associated chronic diarrhea; Toxoplasma gondii, which can cause encephalitis in AIDS patients; and the free-living amebae which cause encephalitis in immune deficient people. In recent years, IWOP has begun serving as a forum for researchers of other neglected pathogens in AIDS patients including the kinetoplastid flagellates Leishmania and Trypanosoma cruzi. IWOP has evolved into a crucial forum for the dissemination of information on diverse and often neglected eukaryotic microbial parasites presenting altered disease profiles in immune compromised patients and other animals. IWOP is regarded as the most important meeting for researchers working on Pneumocystis, Cryptosporidium, and the Microsporidia. Although the opportunistic protists are difficult to study significant advances have resulted from the scientific interactions facilitated by the bi-annual IWOP meetings.